In this case, no. I suspect the use of setq-default comes from a cut and
paste of setting mode-line-format, which is a buffer-local variable, so
setq-default is required to set a default value - setq overrides the
value for the current buffer only.

I tried to re-order the second solution as follows, but it just
displays an "@" in the title bar:
(setq frame-title-format

So far all my emacs tweaks have been made through the customisation
buffers, with a little help from rtfm. Am I right in thinking that
frame-title-format cannot be set via any of the customisation buffers?
Thanks for all your help.
Bernie.